1. Field of the Invention
The present invention is generally in the field of electrical circuits. More particularly, the invention is in the field of frequency synthesizers.
2. Related Art
Modulated frequency synthesizers, such as analog modulated frequency synthesizers, are utilized in cellular communication systems, such as Global System for Mobility (“GSM”) cellular communication systems. In a modulated frequency synthesizer, data is modulated by switching a value of a frequency divider, such as a fractional-N frequency divider, in the feedback path of a phase locked loop. Modulated frequency synthesizers, such as analog modulated synthesizers, often employ a pre-emphasis on the data path to compensate for bandpass filtering caused by the phase locked loop. However, if data pre-emphasis is used, the bandwidth of the loop filter in the modulated frequency synthesizer must be accurately controlled to meet required communication system, such as GSM communication system, specifications.
Modulated frequency synthesizers generally utilize a loop filter that includes passive components, such as resistors and capacitors. These passive components are subject to process and temperature variations, which can cause an undesirable change in the bandwidth of the loop filter. For example, the loop filter typically includes a large capacitor in series with a resistor, where the large capacitor can have a significant undesirable effect on loop filter bandwidth as a result of process and temperature variations.
Thus, there is a need in the art for increased loop filter bandwidth control in a modulated frequency synthesizer, such as an analog modulated synthesizer.